The antioxidant and antimicrobial activities of different phenolic acids grafted onto chitosan

Four phenolic acid-grafted-chitosan conjugates were prepared with different phenolic acids including gallic acid (GLA), caffeic acid (CA), gentisate acid (GTA) and sinapic acid (SA), and their characteristics were analyzed. Furthermore, the antioxidant and antimicrobial activities of conjugates were compared to screen out the optimal conjugates. The characterization analysis showed that the UV absorption peaks of CA-g-CS were stronger than that of GLA-g-CS, indicating a higher substitution degree. In addition, the substitution degree and antioxidant activity of caffeic acid-grafted-chitosan (CA-g-CS) and gallic acid-grafted-chitosan (GLA-g-CS) had significantly ( p  < 0.05) higher than CS and other two conjugates. However, CA-g-CS demonstrated stronger bacteriostatic ability, of which the minimum inhibitory concentrations (MICs) against Pseudomonas aeruginosa , Escherichia coli , Bacillus subtilis and Staphylococcus aureus were lower, and the inhibitory zones were larger than GLA-g-CS. In summary, the present findings will provide a theoretical basis for the expanding of CS application in food processing and preservation.